1. Field of the Invention
The present invention relates generally to flame detection equipment, and more particularly to a flame detection device that decides a flame from an image obtained by photographing a monitoring object with an imager.
2. Description of the Related Art
As prior art methods of processing an image photographed by a monitoring camera and deciding a flame caused by a fire, there are known (1) a method of extracting the infrared rays in a CO2 resonance radiation band which includes wavelengths peculiar to light irradiated from flames, (2) a method of extracting a flame flicker frequency which is a temporal change in the light intensity of the infrared rays in the CO2 resonance radiation band, and (3) a method of extracting the detection of temporal enlargement and reduction which are the spatial behavior of the image of a burning flame. Therefore, prior art flame detection devices which perform image processing are equipped with an entrance window for protecting the interior of the device from dust, dewdrops, etc. The prior art flame detection devices are further equipped with a bandpass filter for extracting the infrared rays in the CO2 resonance radiation band, an imager for photographing an image of the extracted infrared rays, a lens mechanism for projecting the image of a monitoring space onto the imager, and a processing section for processing an image signal output from the imager and deciding a flame caused by a fire.
The CO2 resonance radiation band with a center wavelength of 4.5 xcexcm which is peculiar to flames is suitable for deciding flames because it has a good signal-to-noise ratio (SNR) with respect to external light other than flames. However, infrared-ray imagers for photographing the CO2 resonance radiation band require a complicated cooling structure, etc. Furthermore, the infrared-ray imagers are very expensive and of a large size.
On the other hand, as a method of detecting a flame from the infrared rays in the CO2 resonance radiation band, there is known a prior art flame detector employing a pyroelectric element instead of the infrared-ray imager. The flame detector with a pyroelectric element is structurally simple and inexpensive. However, since the flame detector does not perform image processing, it cannot detect the temporal enlargement and reduction which are the spatial behavior of the image of a burning flame. Because of this, the flame detector is inferior in flame detection accuracy to the image processing method employing the infrared-ray imager.
As an inexpensive imager, there is a charged-coupled device (CCD) imager that is used in an ordinary video photographing machine, etc. The CCD imager is relatively low in price and good in performance. However, in the CCD imager, the wavelength band at which photographing is available is limited to a narrow range from visible light to near-infrared rays (about 1.2 xcexcm) and does not reach the CO2 resonance radiation band which is most characteristic of flames.
In addition, the light energy from flames is at an extremely higher level than the dynamic range of the CCD imager. Because of this, if a flame caused by a fire is photographed with a monitoring camera which employs the CCD imager, halation (signal saturation) will be caused.
In the case where a flame caused by a fire is photographed by the infrared-ray imager, the light energy from the flame will exceed the dynamic range of the imager and cause halation. Therefore, the infrared-ray imager has the same problem as the case of the above-described CCD imager. This halation cannot be suppressed even by aperture control or gain control. Because of this, the CCD imager cannot grasp the spatial behavior of a flame and is therefore unsuitable for the detection and monitoring of flames.
The present invention has been made in view of the circumstances mentioned above. Accordingly, it is an object of the present invention is to provide a small and inexpensive flame detection device which is capable of accurately deciding a flame using a CCD imager. Another object of the invention is to provide a flame detection device that is capable of easily enhancing gray-scale resolution for a flame image when employing an imager. Still another object of the invention is to provide a small and inexpensive flame detection device that makes it possible to decide a flame with a high degree of accuracy by combining an infrared sensor such as a pyroelectric element with a CCD imager.
To achieve the above objects and in accordance with the present invention, there is provided a first flame detection device for detecting a flame caused by a fire, comprising a light attenuation filter for attenuating 90% or greater of light with wavelengths in a visible to near-infrared band radiated from the flame. The first flame detection device further comprises an imager for photographing an image of the attenuated light incident thereon, and a processing section for deciding the flame from the image obtained by the imager.
In the first flame detection device of the present invention, 90% or greater of the light that is incident on the imager is attenuated by the light attenuation filter so that the quantity of the incident light is within the dynamic range of the imager. Therefore, when a flame is photographed, halation that occurs in conventional flame detection devices employing an imager can be prevented, and the spatial behavior of a flame can be grasped from an image obtained by the imager. Thus, in the first flame detection device, the sensing of a flame can be made possible by employing an imager which cannot be used in conventional flame detection devices to sense a flame caused by a fire.
In the first flame detection device of the present invention, the imager may comprise a charged-coupled device (CCD) imager. As previously described, the sensitivity of the CCD sensor is in a narrow range from a visible band to about 1.2 xcexcm and does not reach the CO2 resonance radiation band with a center wavelength of 4.5 xcexcm which is characteristic of flames. However, since light in a wide wavelength range (ultraviolet, visible, near-infrared, and infrared ranges) is radiated from a flame, it is sufficiently possible to photograph flames with the CCD sensor. Furthermore, it is known that for the flicker and spatial behavior of a flame, the sensitive band of the CCD imager is similar to the CO2 resonance radiation band. Therefore, it is sufficiently possible to decide a flame with a high degree of accuracy from an image photographed by the CCD image.
The aforementioned light attenuation filter may comprise a neutral density (ND) filter for attenuating 90% or greater of light with a predetermined wavelength in a visible to near-infrared band, and a visible light cutoff filter for cutting off light with a predetermined wavelength or less in a visible band.
In accordance with the present invention, there is provided a second flame detection device for detecting a flame caused by a fire, comprising an infrared bandpass filter for attenuating 90% or greater of light with wavelengths in an infrared band radiated from the flame. The second flame detection device further comprises an infrared imager for photographing an image of the attenuated light incident thereon, and a processing section for deciding the flame from the image obtained by the infrared imager.
The second flame detection device uses an infrared imager which has sensitivity in the CO2 resonance radiation band, and 90% or greater of the infrared rays that are incident on the infrared imager is attenuated by infrared bandpass filter for attenuating 90% or greater of light. Therefore, an image signal (pixel signal) with a gray level value corresponding to infrared rays radiated from a flame is obtained making the best use of the dynamic range of the infrared imager. As a result, the resolution for the image signal can be easily enhanced, and a flame decision can be performed based on high-accuracy image processing.
Further in accordance with the present invention, there is provided a third flame detection device for detecting a flame caused by a fire, comprising a light attenuation filter for attenuating 90% or greater of light with wavelengths in a visible to near-infrared band radiated from the flame. The third flame detection device also includes an imager for photographing an image of the attenuated light incident thereon; a specific-wavelength transmitting filter for transmitting light with wavelengths in a CO2 resonance radiation band; and an infrared sensor for receiving the light transmitted through the specific-wavelength transmitting filter, and converting the received light into an electrical signal. The third flame detection device further includes a processing section for deciding the flame from changes in the temporal enlargement and reduction of the image obtained by the imager, and from a flicker frequency obtained from the electrical signal output by the infrared sensor.
In a preferred form of the third flame detection device, the imager comprises a CCD imager. In addition to a flame decision based on the image processing by the CCD imager, the infrared rays in the CO2 resonance radiation band are detected employing the above-mentioned specific bandpass filter and the above-mentioned infrared sensor (e.g., a pyroelectric element, etc.). Therefore, in addition to the advantages of the CCD imager, flame decision accuracy can be easily enhanced at low cost by the direct detection of the infrared rays in the CO2 resonance radiation band.
Further in accordance with the present invention, there is provided a fourth flame detection device for detecting a flame caused by a fire, comprising a light attenuation filter for attenuating 90% or greater of light with wavelengths in a visible to near-infrared band radiated from the flame. The fourth flame detection device also includes an imager for photographing an image of the attenuated light incident thereon. Furthermore, the fourth flame detection device includes (1) a first infrared sensor provided with a first specific-wavelength transmitting filter which transmits light with a first wavelength lower than the center wavelength of a CO2 resonance radiation band, the first infrared sensor being operative to receive the light transmitted through the first specific-wavelength transmitting filter and convert the received light into an electrical signal; (2) a second infrared sensor provided with a second specific-wavelength transmitting filter which transmits light with a second wavelength which is the center wavelength of the CO2 resonance radiation band, the second infrared sensor being operative to receive the light transmitted through the second specific-wavelength transmitting filter and convert the received light into an electrical signal; (3) a third infrared sensor provided with a third specific-wavelength transmitting filter which transmits light with a third wavelength higher than the second wavelength; the third infrared sensor being operative to receive the light transmitted through the third specific-wavelength transmitting filter and convert the received light into an electrical signal; and (4) a processing section for deciding the flame from changes in the temporal enlargement and reduction of the image obtained by the imager, and from a distribution of peaks obtained from the electrical signals output by the first, second, and third infrared sensors.
In the fourth flame detection device of the present invention, in addition to a flame decision based on the image processing performed by the CCD imager, a distribution of three beak intensities in the CO2 resonance radiation band is grasped by the above-mentioned three infrared sensors. Therefore, a flame decision can be performed with a higher degree of accuracy. Each of the above-described flame detection devices of the present invention may comprise an aperture mechanism for adjusting a quantity of incident light. In this instance, the aperture mechanism is able to increase or decrease the quantity of light that cannot be adjusted with the above-described light attenuation filter. For this adjustment, a gain control section may be provided in an amplification section which amplifies a signal which is input to said processing section.
The above and further objects and novel features of the present invention will more fully appear from the following detailed description when the same is read in conjunction with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention.